This invention relates to a process and apparatus for the disposal and handling of waste. More particularly, this invention relates to waste disposal systems that use a transfer station.
Municipal waste handling is a costly problem facing cities and counties. Waste handling technology has become a conglomeration of processes with significant difficulties and serious inefficiencies. In an attempt to realize economies of scale, current facilities are built as large as possible, resulting in huge amounts of traffic, noise and odors. While this may be marginally acceptable in a remote landfill site, this is clearly not the case for transfer stations in an urban area. The traffic, noise and odors dramatically reduce the potential waste handling sites in a community. The need to build to suit maximum projected waste loads far into the future further increases costs and limits available sites. The history of waste handling shows that building facilities based on future projected demand is both expensive and risky.
The handling of municipal waste has changed dramatically as a result of environmental factors, demographic shifts, geographical considerations, and social and regulatory changes. As recently as twenty years ago, the majority of waste was delivered to small landfills adjacent to population concentrations in the same vehicles that collected the garbage from individual homes and businesses. As these landfills reached their capacity, and as environmental difficulties from ground water contamination and the like caused additional closures, a trend towards large landfills distant from population centers emerged. This trend gave rise to the development of transfer trailers, large semi-trailers that were used to carry the waste the often hundreds of miles distant from the population centers to the safe modern landfills. To service these trailers, transfer stations were developed. Transfer stations typically comprised large buildings with unloading areas for collection vehicles, tipping floors to allow the accumulation of trash, and pits into which the transfer trailers would drive to be loaded. The trash is loaded by pushing the waste with large bulldozers from the tipping floor through slots located above the transfer trailers into these transfer trailers.
Each of the areas in this type of transfer station must be sized to accommodate large fleets of collection vehicles and transfer trailers, as well as large amounts of accumulated uncompacted trash. Without excess capacity in each operation of the system, it is impossible to accommodate fluctuations in either the rate at which trash is accumulated, or the rate at which the trailers can ship it out. In addition, large numbers of equipment operators are required to ensure that peak capacity is available, even though these operators are not required the majority of time.
The large required land areas, noise, dust, exposed trash, vermin and traffic of typical transfer stations makes them poor neighbors. This, in turn, makes the siting of transfer stations a difficult community problem. The long-term projections of waste flow and large capital cost which must be paid by the community being served make the risk to existing ratepayers a frequent complaint.
More recently, two other trends have influenced the requirements for transfer station design. They are the modern, highly productive collection vehicles and the requirements for recycling. While seemingly different, these trends have the same effect on planning of transfer stations locations. Given the cost of the modern collection vehicle, the time spent travelling to and from the collection area is unproductive, both for equipment and crew. Thus, for efficient operation, it is desirable to locate the transfer station as close to the service station as possible. Likewise, the curbside recycling programs require additional vehicle operations, and thus suffer even more when the transfer station is located at some distance from the collection area. The conventional transfer stations large sites and problems with neighbors dictate against the location of such facilities close to the population centers that they serve.
There have been several attempts to address the failings of the current transfer facilities, and to improve their efficiency. Some facilities are using large compactors that form bales that are placed on the transfer trailers. These units, while allowing formation of accurately weighed loads, do not solve the problem of the mismatch in the process rates. If there is no trash present, the system cannot operate, and if a transfer trailer is not available for immediate removal of the formed bale, the process also stops. Since the same piston that compacts the waste at high pressure is also used to unload the compacted trash onto the trailer, the compactor requires a large high-pressure cylinder with a very long stroke, which is both slow and expensive. In a similar approach, Foster U.S. Pat. No. 5,044,870 describes a system where bulk material is compacted and moved onto a trailer by means of a walking floor. This system suffers from the same delay problems as the compacted bale system described above.
Quante U.S. Pat. No. 4,123,970 describes a system where trash is dumped into a number of hoppers, the weight of the contents of each hopper being determined by weighing the collection vehicle prior to dumping. A control system then selects from the appropriate hoppers by dumping them onto a conveyer to feed a compactor to produce bales of trash. The unit comprising the compactor with rotating pressing boxes and unloading plunger does not address the issues of holding large volumes of uncompacted waste from the delivering collection vehicles. Nor does this system provide the means necessary to separate the compacting and loading operations so as to accommodate wide variations in waste feed rate and shipping rate. Indeed, Quante is silent on the trailer loading and shipping aspects of transfer station design.
A further inefficiency of compactor transfer stations is that they are not integrated with the landfill operations. Even though the compactors have the ability to produce large stable briquettes (industry term for a bale of material compressed beyond its elastic limit so as to not require banding or strapping) that are of greater density than the landfills, the briquettes are broken apart at the landfill. This requires expensive compaction equipment, and the crews involved to make sure that the trash is contained within the landfill site and does not become litter on adjacent properties. These requirements are a substantial expense, which ultimately must be paid for by the individuals being served in each community that ships waste to the landfill.
It is an object of the present invention to provide a process that reduces the exposure of trash to the environment, thus controlling odors, blown trash, vermin, and other environmental problems. Another object of the invention is to provide a process where the compactor stage of the process can operate continuously as waste is received at the transfer station, unloading the baled waste into shuttle containers without the requiring transfer trailers to be available. Yet another object of this invention is to provide a process where transfer trailers can be loaded from the shuttle containers independently of the operation of the rest of the process, so that the transfer trailers do not have to wait for loads to be formed before transporting the waste to the landfill. In this manner, the efficiency of the transfer trailer fleet operation can be increased.